1. Field of the Invention
Disclosed embodiments relate to three-dimensional inductors.
2. Description of the Related Art
An inductor usually consists of a coil of conducting material, typically insulated copper wire, wrapped around a core either of plastic or of a ferromagnetic material; the latter is called an “iron core” inductor. The high permeability of the ferromagnetic core increases the magnetic field and confines it closely to the inductor, thereby increasing the inductance. Low frequency inductors are constructed like transformers, with cores of electrical steel laminated to prevent eddy currents. “Soft” ferrites are widely used for cores above audio frequencies, since they do not cause the large energy losses at high frequencies that ordinary iron alloys do. Inductors come in many shapes. Most are constructed as enamel coated wire (magnet wire) wrapped around a ferrite bobbin with wire exposed on the outside, while some enclose the wire completely in ferrite and are referred to as “shielded”. Some inductors have an adjustable core, which enables changing of the inductance. Inductors used to block very high frequencies are sometimes made by stringing a ferrite bead on a wire. Small inductors can be etched directly onto a printed circuit board by laying out the trace in a spiral pattern. Some such planar inductors use a planar core.
FIG. 1 shows a top view of a conventional spiral multi-turn inductor 100. The inputs of the spiral multi-turn inductor 100 can have polarity due to the lack of symmetry. Since the inductance value of the inductor 100 can be proportional to the total series metal length used to form the inductor 100, the inductance value can be affected by the width of the metal conductor forming the inductor turns, the space between the turns, the diameter of the metal conductor and the number of turns in the spiral. As shown in FIG. 1, the inputs to the inductor 100 can be on opposite sides of the structure. The inputs can be brought out to the same side of the inductor structure. The spiral multi-turn inductor 100 includes a multi-turn spiral portion 102, a first input 104 and a second input 106 which is brought out from the spiral ending point 108 to the opposite side of the inductor 100 from the first input 104. A lead 110 is used to bring the second input 106 out from the spiral ending point 108 of the inductor 100. The spiral multi-turn inductor 100 also has overlap regions 112 and 114 due to its multi-turn portion 102 crossing the lead 110 which can cause capacitive coupling between the layers. The capacitive coupling of these overlap regions 112, 114 can degrade the performance of the inductor 100. Further, the area of the inductor 100 can be proportional to a required quality factor.
FIG. 2 illustrates a perspective-view of a conventional three-dimensional solenoid inductor 200. The three-dimensional inductor 200 comprises series of conductive traces 204 and bonds 206 forming a continuous conductive path from a first port 208 to a second port 210 of the inductor 200. The exemplary three-dimensional inductor 200 has two loops formed by the bonds 206 and the conductive traces 204 forming a solenoid-like shape. A three-dimensional inductor of this structure can have more or less loops as desired. Passing a current through the inductor 200 forms an electromagnetic field in the area within the loops. A three-dimensional solenoid can be limited to reduce area.